Aging skin is the result of more than just chronological age. Skin is exposed to various environmental stresses, such as UV rays, which cause free radicals to form in the skin. Free radicals include, for example, singlet oxygen, hydroxyl radical, the superoxide anion, nitric oxide and hydrogen radicals. Free radicals attack DNA, membrane lipids and proteins, generating carbon radicals. These in turn react with oxygen to produce a peroxyl radical which may attack adjacent fatty acids to generate new carbon radicals. This process can lead to a chain reaction producing lipid peroxidation products. Damage to the cell membrane can result in loss of cell permeability, increased intercellular ionic concentration and/or decreased ability to excrete or detoxify waste products. The end result is a loss of elasticity of the skin and the appearance of wrinkles leading to premature aging of the skin. This process is commonly referred to as photo-aging.
The degree of UV protection afforded by a composition is directly related to the amount and type of sunscreen actives present therein. The more sunscreen actives present, the greater the degree of UV protection. However, in order to incorporate significant amounts of sunscreen actives into a composition, a large amount of emulsifiers need to be used in order to make the composition stable so as to avoid separation and precipitation of ingredients. The use of significant amounts of emulsifiers, while making the composition more stable, detracts from the texture and feel of the composition when applied onto a keratinous substrate.
Compositions having two separate phases, a water phase and an oil phase, that emulsify readily by agitation are generally referred to by the term “two-phase composition.” They differ from emulsions by the fact that at rest the two phases are separate instead of being emulsified in one another. Thus, the two phases are separated at rest by a single interface whereas, in emulsions, one of the phases is dispersed in the other in the form of a multitude of droplets, and the interfaces are therefore multiple, those interfaces generally being stabilized by emulsifying surfactants and/or emulsifying polymers. The use of two-phase compositions requires prior agitation in order to form an extemporaneous emulsion. This must be of sufficient quality and stability to allow a homogeneous application of the two phases, but such that at rest, the two phases rapidly separate and regain their initial state, this phenomenon being better known by the term “phase separation.”
A number of known two-phase compositions form, after agitation, an opaque emulsion, which is a mixture of two phases that are immiscible in one another. However, these compositions are generally presented in transparent containers, and the opacity of the two emulsified phases is aesthetically unpleasant. Moreover, it is increasingly sought to use transparent compositions because, just like water, the transparency is a symbol of purity and therefore of cleanliness, and transparent compositions are thus particularly appreciated by the users.
The use, in two-phase compositions, of silicone oils, such as, for example, cyclopentasiloxane make it possible to obtain compositions that form, after agitation, a transparent mixture of two immiscible phases. However, it is difficult to obtain a transparent mixture when the two phases are not miscible, without using cyclic silicone oils.
Sunscreen actives are relatively polar and can cause preservatives to migrate from water phases to oil phases. This results in difficulty in preserving sunscreen formulations and can require high levels of preservatives. The high levels of preservatives can be harsh to human skin.
Conventional sunscreen compositions are expected to possess water-resistance properties in order to inhibit the protective composition from being easily removed from a keratinous substrate by sweat and exposure to water. In order to achieve this function, film-formers are typically employed in the composition. By forming a film on the surface of keratinous substrates, the sunscreen actives are more steadfastly held in place upon exposure to water. The use of film-formers; however, has a negative impact of the tactile properties of the composition, making the composition feel tacky to the user.
Multiple phase sunscreen compositions have been attempted in the art. For example, EP 831765, which is hereby incorporated by reference in its entirety, discloses a multi-phase sun screen composition, its production, and its application to the skin. EP 831765 includes at least two oily phases that are separate and are mixed prior to use on the skin. When mixed, the UV filters remain in the phase for which they were originally added. However, the sun screen composition of EP 831765 does not include water phases or an emollient combination resulting in a transparent composition having desirable sensory features.
WO/2003070201 and WO/2003070202, which are hereby incorporated by reference in their entirety, disclose a two-phasic sunscreen preparation comprising water/oil emulsions. The two-phase element includes a water/oil emulsion and a lipophilic phase. An emulsifier is included due to the inclusion of the water/oil emulsion. At least one of the two phases is not transparent, thus, it is not capable of being used in transparent applications.
WO/2010006995, which is hereby incorporated by reference in its entirety, discloses a silicon-free transparent two-phase composition. The composition includes an oil phase and a water phase, where both phases are initially transparent. Upon agitation, the two phases form a mixture that is transparent. To achieve such transparency the two-phase composition is formulated such that the reflective index of the oil phase and the water phase are substantially equal and result in a high amount of polyol (at least about 40%) being used. Such high loadings of polyol result in undesirable cosmetic features, such as an oily, a tacky or a heavy feel.
Thus, it is an object of the present invention to provide a composition and process for protecting cellular targets from aging and photo-damage caused by UV light, in general, and free radicals formed thereby, in particular.
It is yet another object of the present invention to provide a sunscreen composition which provides a significant degree of UV protection, while at the same time having a light, non-oily texture and skin feel property.
It is yet another object of the present invention to provide a sunscreen composition which possesses water-resistance properties but does not require the use of a film-former.
It is yet another object of the present invention to provide a sunscreen composition that is made up of two separate phases that are transparent and return to transparency after complete separation.
It is yet another object of the present invention to provide sunscreen composition which provides a significant degree of UV protection and is preservative free.